1. Field of the Invention
This invention relates generally to large aperture lightweight antennas. Such antennas are especially suited for use on lighter than air platforms. More particularly, this invention is especially well suited to provide inflatable and collapsible transreflector antennas.
2. Related Art
Lighter-than-air (LTA) vehicles such as manned airships (blimps), unmanned airships, or tethered aerostats have been used as platforms for radar and radio communication relays. However, since LTA lift capacity is reduced as the vehicle operates at higher altitudes, LTA vehicles require extremely lightweight antenna systems to function in this role at very high altitudes. Adding to the complexity of such antenna installations is the requirement for ballonets, or buoyancy control systems, to control the lifting force and allow controlled ascent and descent of the LTA vehicle. As the maximum altitude of the LTA increases, these ballonets occupy a larger fraction of the total volume within the LTA envelope. Ideally, the antenna would be collapsed or folded when the LTA is at low altitude (ballonets fully expanded) and the antenna would be fully deployed when the LTA is at high altitude (ballonets fully collapsed).
Scanning antennas utilizing transreflectors of spherical, parabolic, elliptical, or other toric sections are described in U.S. Pat. No. 2,835,890—Bittner, U.S. Pat. No. 2,989,746—Ramsay, and U.S. Pat. No. 4,214,248—Cronson et al. However, these antennas are not designed to be collapsible, are fabricated from thick metal rods or wires, or are comprised of multiple singly curved, reflective/transmissive surfaces. An inflatable spherical reflector is described in U.S. Pat. No. 4,364,053—Hotine but it is not collapsible nor capable of 360 degree scanning. A planar inflatable/collapsible antenna is described in U.S. Pat. No. 5,132,699—Rupp.
Although no published documentation is presently in hand, it is also believed others have previously recognized that an RF reflective conductive surface can have a thickness less than one RF skin depth.
A collection of possibly relevant prior art documents are identified below:                [1] K. S. Kelleher and H. H. Hibbs, “A New Microwave Reflector,” NRL Report 4141, May 1953.        [2] J. D. Barab, J. G. Marangoni, and W. G. Scott, “The Parabolic Dome Antenna: A Large Aperture, 360 Degree, Rapid Scan Antenna, Toroidal Microwave Reflector,” IRE National Convention Record, Part 1,1956.        [3] J. Ruze, “Lateral-Feed Displacement in a Paraboloid,” IEEE Transactions on Antennas and Propagation, Vol. AP-13, Sep. 1965, pp. 660–665.        [4] A. V. Mrstik, “Scan Limits of Off-Axis Fed Parabolic Reflectors,” IEEE Transactions on Antennas and Propagation, Vol. AP-27, September 1979, pp. 647–650.        [5] T. Li, “A Study of Spherical Reflectors as Wide-Angle Scanning Antennas,” IEEE Transactions on Antennas and Propagation, Vol. AP-7, July 1959, pp. 223–226.        [6] G. Peeler and D. Archer, “A Toroidal Microwave Reflector,” IRE National Convention Record, 1954, pp. 242–247.        [7] C. J. Sletten, Reflector and Lens Antennas, Massachusetts, Artech House, 1988.        [8] M. Gilbert and N. Williams, “A Hybrid Antenna System Incorporating a Parabolic Torus, “Proceedings of the IEE Conference on Antennas and Propagation, 1985, pp. 146–150.        [9] D. Paolina,” Reflector Antennas Analysis Notes,” NWC Technical Memorandum 5352, August 1985.        [10] A. W. Love, Antenna Engineering Handbook, New York, McGraw-Hill, 1984, Artech House, 1988.        [11] S. P. Applebaum, “Adaptive Arrays,” IEEE Transactions on Antennas and Propagation, Vol. AP-24, September 1976, pp. 585–598.        [12] S. Silver, Microwave Antenna Theory and Design, London, Peter Peregrinus Ltd., 1984.        [13] U.S. Pat. No. 4,214,248—Cronson et al.        [14] U.S. Pat. No. 2,835,890—Bittner.        [15] U.S. Pat. No. 2,989,746—Ramsay.        [16] U.S. Pat. No. 4,364,053—Hotine.        [17] U.S. Pat. No. 5,132,699—Rupp et al.        [18] K. S. Kelleher and H. H. Hibbs, “A New Microwave Reflector,” NRL Report 4141, May 1953.        [19] J. D. Barab, J. G. Marangoni, and W. G. Scott, “The Parabolic Dome Antenna: A Large Aperture, 360 Degree, Rapid Scan Antenna, Toroidal Microwave Reflector,” IRE National Convention Record, Part 1, 1956.        